Hydrocarbon derivatives of lead and their preparation



Patented Mar. 6, 1934 i HYDROCARBON DERIVATIVES OF LEAD AND THEIR PREPARATION Gellert Alleman, Walllngford, Pa., asaignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application January 18, I929,

Serial No. 333,512 r 23 Claims. (Cl. 260-11) This invention-relates to alkyl oraryl derivatives of lead and their preparation, and more particularly to the preparation of higher alkyl derivatives such as the tetra amyl or other amyl compounds of lead.

The alkyl and aryl derivatives of various elements, both metallic and non-metallic have been found useful'in preventing the knock of gasoline or kerosene when used in high compression internal combustion engines. The most commonly used of these compounds is tetra ethyl lead, which, when used in quite small quantities in solution in fuels which normally knock when used under high compression, raises the critical com pression to such an extent as to completely eliminate the objectionable detonation of the fuel mixture.

When the compounds heretofore known are used detonation is prevented as described above, but only when the fuel actually being exploded contains the compound in solution. I have found, however, that when amyl derivatives of lead are used, the anti-knock effects persists for a considerable time after the introduction of the derivative has been stopped and while gasoline containing no anti-knock material is being used as'fuel, this result being apparently due to the deposition or retention within the cylinder oi some residue of the amyl lead used or the presence therein of colloidal lead.

Formerly, the cost of the amyl alcohols, the only sources of the amyl radical available, appeared to eliminate amyl derivatives entirely from consideration as practical anti-knock materials; The present commercial production of pentanes from natural gas and their ready halogenation to amyl halides renders the production of amyl derivatives commercially possible and it is now feasible to use such derivatives in admixture with fuels without undue increase of cost of production;

Attempts to apply the methods used in the preparations of the lower alkyl derivatives of various elements such as lead to the production of amyl derivatives have been unsuccessful since not only is a difference of reactivity exhibited but separation of any amyl derivatives from the products of reaction, even though their formation may be suspected, has been found to be impossible. The only successful method of separation of ethyl derivatives, for example, is distillation in steam. The amyl derivatives are either not volatile, for example the normal tetra amyl derivative 'of lead, or relatively slightly volatile in steam and they decompose upon heating prior to reaching their boilingpoints. The tetra amyl leads, for example, decompose violently, though not explosively, on heating even in a vacuum;

One object of the present invention is the pro vision of a method adapted particularly to the higher alkyl derivatives of lead in which high yields of the desired derivatives are obtained, the by-products of the reaction being of such character that the derivative may be obtained by extraction by solvents from the residue of the reaction. While, because of the results outlined, the advantages of the present method are most striking when derivatives of radicals such asamyl are prepared, high yield of lower alkyl and aryl derivatives are also obtained and in mixtures rendering their separation particularly easy.

Afurther important object of the present inventon is the production of derivatives containing colloidal lead which itself acts as, an effective anti-knock, as will be pointed out below, and augments the effects of the derivatives containing it. Colloidal lead thus produced also appears to contribute to the persisting anti-knock effect noted above.

In order to illustrate the practice of the improved method the preparation of tetra. amyl lead will be firstdescribed. An amyl halide, or a mixture of amyl halides, is used as the source of the amyl radicals. While the various tetra amyl lead compounds difier considerably in their actions as anti-knock compounds, the tetra diethyl methyl lead, for example, being more effective than the tetra normal amyl lead, for the sake of economy mixtures of the various amyl halides obtained either from the ordinary mixture of alcohols or from the mixed pentanes may be employed. The various products are similar and may be separated. Using commercial 1 amyl alcohol, containing isobutyl carbinol and secondary butyl carbinol, for example, as the source of the amyl chlorides, there would be obtained a mixture of the corresponding lead derivatives.

The reaction vessel, which may be glass or metal lined with glass or enamel, is preferably provided with three spaced necks, one receiving a' mechanical stirrer, another the lower end of a reflux condenser, and the third a feed-funnel for the gradual addition of the reagents. It is also desirable to provide some means for heating and cooling the vessel, for example, an internal or external coil through which steam may be passed for heating or cold water, brine or liquid ammonia for cooling.

' In carryingout the preparation, 24.36 parts of metallic magnesium are introduced into the vessel together with 138.91 parts of lead chloride and a few crystals of iodine which act as a catalyst in contact with the magnesium. Equivalent quantitles of other reactive anhydrous lead compounds may, of course, be used.

There is theoretically required in the reaction one molecule of an ether for each atom of magnesium present. The ether used is a matter of ch ic Since it does not affect the character 0! the product, and it is found convenient to use either diethyl or diamyl ether, the proper amount of the former being 74.08 parts and ot the lat er 158.17 parts. Since a solvent is necessary for the reaction products, it is advisable to use about four times the quantities of ethers mentioned. On the other hand the theoretical amount of either ether may be used and some other solvent employed. For example, ifdiethyl ether is used in the theoretical amount, solvents such aspentane and its isomers or amylene and its isomers may be employed either'in whole or in part as solvents. Ii diamyl other is used benzene, toluene or xylene may be employed, the choice 01' solvents being dictated by reasons of adaptability, boiling points and economy.

The ether or mixed ether and solvent are, added to the materials in the reaction vessel. To the mixture the desired amyl halideis ihen added drop by drop or in a iine stream, 106.53 parts being added it the chloride is used, 151.04 parts it tlie' bromide is used, or 198.05 if the iodide is {Usually the reaction starts spontaneously after a short time althoughit may be accelerated by warming. The reaction is quite violent and takes place with considerable evolution or heat andseparation of metallic lead. It is found that, ii 300 cc. of amyl halide are used, its addition should be extended over the period of about one hour accompanied by continuous vigorous stirring. About one hour is required to complete this initial reaction.

The whole mass is then cooled by means of ice water, or, in the case of large quantities, by brine or liquid ammonia to approximately 0 C. and cold water or dilute HCl is added drop by drop or in asmall stream. The reaction is very violent and continuous cooling is necessary. when the re-v ac. ion has subsided, the tetra amyl lead is found dissolved in the ether or solvent which separates on the top of the reaction mass. Additional ether may be added to extract additional tetra amyl lead. The ethereal solution is separated, filtered, and the ether distilled, leavingimpure tetra amyl lead in the receptacle. This residue is then heated to C. under vacuum when a yellow solid tetra amyl lead is then filtered and treated with absolute ethyl alcohol. The impurities. (unchanged amyl chloride, etc., are soluble in the alcohol whereas tetra amyl lead is substantially insoluble. Accordingly, the relatively pure tetra amyl lead containing colloidal lead may be separated and dried, if desired, by contact with anhydrous calcium chloride.

The use oi'dilufe HCl in the reaction above is found advantageous since soluble magnesium chloride is formed rather than a cake of insoluble magnesium hydroxide which makes diiiicult treatment 01' the mixture with solvents.

As an alternative method for the recovery of the compound from the reaction mass, the other may bedistilled from the reaction vessel and the remaining material treated with low boiling gasoline (i'reed from sulphur compounds). The gaso-'.

line solution is then removed and the gasoline evaporated leaving impure tetra amyl lead, containing colloidal lead, which maybe purified in the manner described above.

Ii ether alone is used as the solvent, it is ad- .visable toextract' the residual mass in the. reaction vessel with low boiling gasoline in order to recover the last traces of tetra'amyl lead.

The description above ,reiers generally to the separates. The supernatant liquid containing the preparation of any of the tetra amyl compounds, the only difference noticeable being in respect to the violence of the reaction, the secondary amyl halide reacting more vigorously than the normal halide and the tertiary halide reacting more vigorously than either of the preceding. The bromides are more reactive than the chicrides and the iodides more reactive than the bromides. q

The reaction involved in the first step 01' the above process probably'includes first the formation of the usual magnesium-alkyl-halide-ether compound of the familiar Grignard reaction, followed by the immediate reaction of this compound with the lead chloride present to form a complex alkyl-magnesium-lead-halide-ether compound of unknown composition with separation of metallic lead. The substance initially formed if diethyl ether and amyl chloride were employed would. be (csflioMgCl-o-(CzHsh. If amyl ether was used the compound would be (C5Hi1)MgC1-O-(C5H1i)2. In the second step of the process the alkyl-magnesium-lead-halideether complex referred to above is decomposed by water or dilute HCl with liberation of the tetra 100 amyl lead Pb(C5H11)4.

f As stated above, other than amyl derivatives may be used. For example, methyl, ethyl, propyl, butyl, phenyl or benzyl halides may be used in place of the amyl halide. Likewise other metals or elements may be used instead of lead, for example, thallium, iron or nickel. In eabh case the reaction takes place similarly to that described .above with separation 01! the metal during the first step of the reaction.

(CH3) 2( (CzHs) z-CH) zPb,

being specifically chosen for illustration.

In preparing this compound the reaction is carried out in the same manner as in the preparation oi the tetra amyl derivative described above except that instead of using a single alkyl derivatives mixture oi! equimolecular proportions or methyl and amyl halides are used. To a mixture 01 48.72 parts of metallic magnesium (preferably in the form of an alloy containing 10% copper), 277.82 parts of lead chloride, and 148.16 parts of ethyl ether, (or 316.34 parts of amyl ether), together with an excess of ether or other solvent, there is added a mixture of 106.53 parts of the amyl chloride (diethyl chlor methane) and 141.97 parts 0! methyl iodide in the manner described above, the reaction then proceeding in the same manner as the previously described reaction, and theproducts being similarly separated. In these cases, also, colloidal lead is present in the products.

An alternative method'oi separation by steam. distillation may be applied to the dimethyl diamyl" lead derivatives or to the diethyl diamyl 14? and dried by contact with anhydrous calcium chloride. During such distillation, colloidal lead remains with the residue so that the pure derivative is obtained.

The mixed dimethyl diamyl derivative discussed is an inexpensive member of the group of metallic derivatives containing amyl radicals which have in common various desirable properties later described. The methyl halide used, which may be the chloride, bromide or iodide, and preferably the last because of its higher boiling point, is readily prepared from methyl alcohol by halogenation. In commercial production the chloride would, of course, be cheapest but requires the use of pressure apparatus. The

diethyl chlor methane (or other halogen deriva-' tive) is obtained by halogenation of diethyl methane which occurs in natural gas or by the esterification by a halogen acid of diethyl carbinol.

The reaction may be varied to produce numerous other products not only by varying the alkyl or amyl derivatives used in admixture or the metal, but by varying their proportions. For example, if the product desired were monoethyl triamyl lead, one molecular proportion of ethyl bromide or other halide would be used for every three molecular proportions of amyl halide. Or, supposing dipropyl monoamyl iron to be desired, two molecular proportions of propyl halide would be used for every one of amyl halide.

The described methods differ from the well known Grignard reaction in that the latter is performed in two steps: first, the magnesium alkyl halide is formed and separated and secondly, this compound is treated with the material into which it is desired to introduce the alkyl radical. Inthe present process the magnesiumv alkyl halide is used in the'state, that is, it is formed in the presence of the substance with which it is ultimately to react. By reason of this, the time of the reaction is reduced to less than half that required by the Grignard process, carried out with preformed magnesium alkyl halide, and a much larger yield is obtained, due probably to the fact that the more direct reaction eliminates the formation of undesired by-products. The magnesium alkyl halide is,'furthermore, pure and uncontaminated by the products formed by carbon dioxide and moisture from the air, whereas the isolated halide is always rendered impure by these. products prior to use.

In applying my improved reaction to the preparation of mixed derivativesyit might be suspected that the product would be a mixture of two tetra alkyl derivatives: for example, in the preparation described above, a mixture or tetra methyl lead and tetra amyl lead. As a matter of fact, however, the mixed derivative is the primary product.

The derivatives prepared by my improved reaction are characterized by the presence of colloidal metal. While transparent and apparently perfectly clear after filtration, a beam of light directed through the liquid exhibits a smoky path, giving rise to the well known Tyndall effect characteristic of colloidal solutions. It appears that this colloidal metal results from theseparation of the metal in the initial part of the rear ion as-described above, the separation possibly taking place under optimum conditions for the production of the colloidal state. It is probable, also, that some of the colloidal lead results from the decomposition of the tetra alkyl lead.

Since the preparations described above are advantageously carried out using alkyl iodides, and

because of the high cost of iodine, it is desirable to recover the iodine from the reaction residue. This is most readily accomplished by treatthe usual manner commonly employed in its recovery.

It has been mentioned above that there occurs an Q after effect eliminating knocking after the use of gasoline containing derivatives prepared as above. In an experiment to determine the cause of this effect, the cylinder walls and heads of an engine were cleaned and the engine operated using as fuel a gasoline which would normally produce knocking containing a small amount of tetra amyl lead prepared in accordance with the above method. Knocking was entirely eliminated. The cylinders were then opened and the walls and heads found to contain a deposit which was found under the microscope to have a metallic appearance and consist of evenly arranged particles having the appearance of small piles of microscopic shot. These deposits were removed and shaken up in highly purified gasoline which did not show the Tyndall effect. A suspension of colloidal lead which did show the Tyndall effect was thus produced. Positive tests for lead were obtained upon chemical examination of the deposits. The amount of the deposit indicated that the lead deposited in the cylinder'was not solely derived from that present in the colloidal state in the lead derivative but contained lead produced by the decomposition of the derivative.

Decomposition of the amyl derivatives by heat results in the formation of large amounts of colloidal lead. This is especially noticeable in. the case of the dimethyl di-diethyl methyl lead described above which at 188 C. decomposes completely with separation of colloidal lead in considerable amounts. In fact, during such decomposition (produced by dropping the dimethyl diamyl lead into a tube maintained at 188 C.) the lead separating in the colloidal state exceeds the amount separating in a larger state of aggregation. .Similar decompositions take place when corresponding derivatives of other metals are heated.

In order to determine the anti-knock efiect of colloidal lead, the lead produced in this manner was shaken up in purified gasoline having pronounced knocking effects and the product filtered through a fine filter. The colorless and apparently clear filtrate exhibited the Tyndall effect and when used in an engine was found to have a high anti-knock value. Other colloidal .metals, for example, thallium, iron and nickel,

exhibit similar effects.

The duration of the anti-knock effect was determined by an experiment in which 1.25 cc. of dimethyl di-diethyl methyl lead in a liter of gasoline, was used in an engine. engine was stopped and the gasoline removed. After fifteen hours the engine was operated using a fuel having knocking characteristics. Knocking was found to be entirely eliminated, due apparently, to the colloidal lead remaining in the cylinders from the previous run.

It will be seen that my'improved process results in the convenient preparation of heretofore unknown hydrocarbon derivatives and also in the introduction into these derivatives of colloidal metals, very desirable impurities when the derivatives are to be used as constituents of gasoline to prevent knocking. The products, furthermore, which are produced by this method serve not only as anti-knock substances but are particularly After a run, the

desirable by reason of their pers sting after effect. They also provide economical sources of large quantities of colloidal'metals which in themselves serve as anti-knocks.

. It will be understood that the term diethylmethyl in the claims refers to the amyl radical described above.

What I claim and desire to protect by Letters Patent is:

1. A compound having the general formula RiPb in which the Rs represent hydrocarbon radicals, at least one of which is a diethylmethyl radical.

2. A compound having the general formula RiPb in which the R's represent hydrocarbon radicals, at least two of which are different, and at least one of which is a diethylmethyl radical.

3. A compound having the general formula RiPb in which the Rs represent hydrocarbon radicals, at least two of which are diethylmethyl radicals.

4. A compound having the general formula R-iPb in which the Rs represent hydrocarbon radicals, at least two of which are different, and at least two of which are diethylmethyl radicals.

5. A compound having the general formula RAPb in which the R's represent hydrocarbon radicals, at least two of which are different, and at least two of which are diethylmethyl radicals, the others being alkyl radicals.

6. Dimethyldidiethylmethyl lead.

'7. A composition including a compound having the general formula RiPb in which the R's represent hydrocarbon radicals, at least one of which is a diethylmethyl radical, and colloidal lead.

8. A composition including a compound having the general formula RAPb in which the Rs represent hydrocarbon radicals, at least two of which are diethylmethyl radicals, and colloidal lead.

9. A composition including dimethyldidiethylmethyl lead and colloidal lead.

10..I'he process oi producing a mixed amyl derivative of lead, which includes effecting the reaction of a lead salt with a mixture of magnesium-hydrocarbon-halide compounds containing different hydrocarbon radicals, at least one of 'which is an amyl derivative, and decomposing theintermediate product thus formed to produce the ainyl derivative of lead.

11. The process of producing a mixed hydrocarbon derivative of lead, which includes effecting the reaction of a lead salt with a mixture of magnesium-hydrocarbon-halide compounds containing different hydrocarbon radicals, and decomposing the intermediate product thus formed to produce the hydrocarbon derivative of lead.

12. The process of producing a diethylmethyl compound of lead, which includes effecting the reaction of a lead salt with at least one magnesium-hydrocarbon-halide compound, said one compound being a diethyhnethyl compound, and decomposing the intermediate product thus formed to produce the diethylmethyl compound of lead.

13. The process of producing a mixed diethylmethyl compound of lead, which includes effecting the reaction of a lead salt with a mixture of magnesium-hydrocarbon-halide compounds, at least one of which is a diethylmetlnrl compound, and decomposing the intermediate product thus formed to produce the diethylmethyl compound of lead.

14. The process of producing dimethyldidiethylmethyl lead, which includes elfecting the reaction of a lead salt with a mixture of magnesiummethyl-halide and magnesium-diethylmethylhalide, and decomposing the intermediate product thus formed to produce dimethyldidiethylmethyl lead.

15. The process of producing dimethyldidiethylmethyl lead, which includes adding a mix ture of diethylchlormethane and methyl iodide in substantially equimolecular proportions to a mixture of magnesium, lead chloride and ether, and decomposing the intermediate product thus formed to produce dimethyldidiethylmethyl lead.

16. The process of producing dimethyldidiethylmethyl lead, which includes adding a mixture of diethylmethyl halide and methyl halide in substantially equimolecular proportions to a mixture of magnesium, a lead salt and an ether, and decomposing the intermediate product thus formed to produce dimethyldidiethylmethyl lead.

17. The process of producing a mixed hydrocarbon compound of lead, which includes adding a mixture of hydrocarbon halides containing different hydrocarbon radicals to a mixture of magnesium, a lead salt, and an ether, and decomposing the intermediate product thus formed to produce the hydrocarbon compound of lead.

18. The process of producing an amyl compound of lead which includes reacting a lead salt with at least one magnesium-hydrocarbon-halide compound simultaneously with the formation of the latter, said one compound being an amyl compound, and decomposing the intermediate product thus formed to produce the amyl compound of lead.

19. The process of producing a mixed a'myl compound of lead which includes reacting a lead salt with a mixture of magnesium-hydrocarbonhalide compounds simultaneously with the formation of the latter, at least one of said compounds being an amyl compound, and decomposing the intermediate product thus formed to produce the amyl compound of lead.

20. The process of producing a mixed hydrocarbon compound of lead which includes reacting a lead salt with a mixture of magnesiumhydrocarbon-halide compounds containing different hydrocarbon radicals simultaneously with the formation of such compounds, and decomposing the intermediate product thus formed to produce the hydrocarbon compound of lead.

salt with at least one magnesium-hydrocarbonhalide compound simultaneously with the formation of the latter, said one compound being a diethylmethyl compound, and decomposing the intermediate product thus formed to produce the diethylmethyl compound of lead.

22. The process of producing a mixed diethylmethyl compound of lead which includes reacting a lead salt with a mixture of magnesium-hydrocarbon-halide compounds simultaneously with the formation of the latter, at least one of said compounds being a diethylmethyl compound, and decomposing the intermediate product thus formed to produce the diethylmethyl compound of lead.

23. The process of producing dimethyldidiethylmethyl lead which includes reacting a lead. salt with a mixture of magnesium-methyl-halide and magnesium-diethylmethyl-halide simultaneously with the formation of said halides, and decomposing ,the intermediate product thus formed to produce dimethyldidiethylmethyl lead.

GELLERT ALLEMAN. 

